PROJECT SUMMARY ABSTRACT Dr. Weisberg is a Clinical Pathologist and Physician Scientist investigating the unique immune microenvironment within human pancreas. Immune regulation within tissues is highly dependent on non- recirculating resident immune cells. Tissue macrophages modulate local immune function, sense metabolic disturbances and participate in tissue repair and homeostasis, and tissue resident memory T cells (Trm) provide localized protective immune responses and tissue immune surveillance. Populations of Trm have now been identified in almost all tissues of the body. Human and murine studies show that Trm are phenotypically, transcriptionally and functionally distinct compared to circulating T cells. Although core properties of Trm common to most tissue sites have been identified, the differentiation state and functional profiles of Trm are also shaped by their microenvironment. These tissue specific properties of Trm and how they are altered by local stressors are less well defined. Due to the limited availability of healthy human pancreas tissue, relatively little is known about the resident immune cells of human pancreas. More knowledge is needed about these cells, because disruption of pancreatic immune homeostasis has severe consequences for human health, leading to diseases with high morbidity and mortality including acute and chronic pancreatitis, type I diabetes and pancreatic cancer. Obesity is associated with pro-inflammatory changes in pancreas and is a major risk factor for pancreatitis and pancreatic cancer. Elucidating the mechanisms that regulate pancreas resident immune cells and how they are influenced by metabolic stressors such as obesity may suggest novel strategies to prevent and treat pancreatic disease. Using a resource within Dr. Donna Farber?s lab which provides access to multiple gastrointestinal tissues from previously healthy organ donors, our preliminary studies have already defined several unique properties of pancreatic Trm. Within pancreas, networks of CD8 Trm cluster with macrophages in the exocrine and ductal areas, surrounding but not penetrating into the endocrine islets. The Trm are resting but with high functional capacity, and the macrophages express mediators of both positive and negative T cell regulation. Our central hypothesis is that pancreatic Trm are maintained in a state distinct from other sites by their local interactions with pancreatic macrophages; and due to their residence in a key tissue that regulates and senses metabolic changes, pancreatic Trm are uniquely sensitive to metabolic alterations such as obesity. The aims of the proposal are 1) Define the distinct properties of Trm in pancreas compared to neighboring tissues; 2) Identify mechanisms of pancreatic Trm-macrophage crosstalk; 3) Identify obesity-related changes in pancreas Trm functional profiles and localization. This career development award will provide critical training and experience in human T cell immunology research, and computational analysis of high dimensional immune data allowing Dr. Weisberg to establish an independent translational immunology research career studying mechanisms of tissue-specific immune regulation.